Wirelessly posted (Samsung Galaxy Nexus: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_3; en-us) AppleWebKit/533.16 (KHTML, like Gecko) Version/5.0 Safari/533.16)
Accorording to the past record of getting SunCom 4 years ago. Customers bought phones in full price (except branded Android phones and NS) are able to keep the current plan.
However, there is a possibility that the customer has to opt for new plan (both prepaid and contract) if the customer has to migrate from CDMA to HSPA; nevertheless, LTE may be another story.
Only time will tell.